1. Field of the Invention
The present invention relates generally to ground transportation systems and, more particularly, to an improved propulsion system for mass transit vehicles which utilizes linear turbine drive apparatus.
2. Description of the Prior Art
Many types of propulsion units have been proposed for use with high speed rail vehicles. A typical arrangement for driving a high speed rail vehicle utilizes a suitable diesel engine or a conventional electric motor that directly drives the wheels of the vehicle. While these arrangements provide generally acceptable performance for low and moderately high speeds, they are impractical for very high speeds, for example, in excess of 200 miles per hour. The reason for this is that extremely smooth and precise tracks are required for passenger ride comfort and adequate power transfer from the wheels to the track, thereby necessitating extensive and continuous track maintenance.
High speed trains presently under development, especially those in the magnetic levitation (MAGLEV) category, are propelled by electric linear motors while magnetic levitation provides guidance and smooth suspension. These high-speed trains require very large investments in guideway construction and associated electric power systems. The electric power systems (consisting of power lines alongside the track and feeder lines from centralized power plants, a.c. frequency converters and speed control stations at intervals along the track, and the active part of the linear electric motor installed in the track) are a major portion of the total guideway cost. In contrast, the cost of the vehicles, even when incorporating sophisticated technologies such as MAGLEV, is a relatively small portion of the total transport system cost. There is, therefore, an economic incentive to replace the electric propulsion system with an on-board propulsion system to make the vehicle less dependent on ground-based infra-structure and more autonomous in propulsion, levitation and guidance.
The economic payoff of a self-contained propulsion system increases with increasing transit distances. Present-day railroad systems corroborate that argument: short-range transit systems typically utilize external electric power, whereas long-range transportation systems utilize autonomous propulsion in form of Diesel locomotives.
The linear turbine drive of the present invention is a propulsion system largely contained within the vehicle and as such provides the desired autonomy in operation. It can also provide indigenous levitation by producing a gascushion.
The linear turbine drive consists of an onboard gas generator, typically an aeronautical fan/jet engine unit, and turbomachinery components oriented in line with the track. Some of the components--a row of nozzle blades and a row of turbine blades--are indigenous to the vehicle. The exhaust stream from the nozzles produces the initial thrust force. A gas deflector rail, the linear equivalent of a stator blade stage in a rotary turbine, is attached to the track. The gas deflector rail is a fence-like structure extending along the track in which the pickets consist of flow turning blades. It serves to deflect into a forward direction the gas stream which was exhausted by the nozzles into a nearly backward direction. The stream is directed into the vehicle-mounted turbine blades to produce additional forward thrust which is of a similar magnitude as the thrust produced by the nozzles. The propulsion system may also include turbine components having an opposite orientation for the purpose of producing reverse thrust for braking and vehicle motion reversal. Control gates are used to selectively operate the propulsion system in the forward or reverse thrust mode. The exhaust from the linear turbine system can also be used in a gascushion providing levitation for the vehicle.
There are a number of patents which disclose railway vehicles utilizing the reaction of gas streams for the purpose of propulsion. They fall into two categories: (I) those where the propulsive gas stream is generated on-board; and, (II) those where the propulsive gas stream is supplied from an external source, e.g. by pipeline and compressors installed along the track. The present invention falls into the first category along with patents U.S. Pat No. 3,547,042 to O'Connor, and U.S. Pat. No. 2,869,479 to Hutchinson.
Patents in the second category include U.S. Pat. No. 4,085,681 to Barber; U.S. Pat. No. 3,242,876 to Berggren; U.S. Pat. No. 3,718,096 to Bloomfield et al.; U.S. Pat. No. 2,228,885 (German file number) to Gantzer; U.S. Pat. No. 3,540,378 to Giraud; U.S. Pat. No. 3,815,866 to Wirth. These patents (with the exception of Bloomfield) combine fluid reaction type propulsion with gas-cushion levitation. Mouritzen's paper entitled "Impulsive-Jet Transportation Systems" published in Mechanical Engineering, Vol. 94, No. Feb. 2, 1972, pages 12-17, also deals with an external high-pressure-air power system.
The Category II systems require a complicated valving system in the pipe network which must be actuated to supply the high pressure air only at the instant the train is passing a particular valve. To minimize gas flow losses these valves must be rather closely spaced. An essential distinguishing feature of the inventions of Category II, however, is that the external power supply does not provide the desired autonomy in propulsion and the associated low cost of construction which is the aim of the present invention.
The patents under Category I, inasmuch as propulsion autonomy can be claimed for them, shall therefore be distinguished from the present invention in more detail. U.S. Pat. No. 2,869,479 to Hutchinson, while based on general fluid stream reaction principles, does not contain turbine-type blades. Instead, Hutchinson describes a multitude of vehicle-based and ground-based conduits which duct the propulsive gas stream backwards from vehicle to ground back to vehicle and so on in a vertically and horizontally undulating flow path. His vehicle is shown to be riding on wheels.
O'Connor's U.S. Pat. No. 3,547,042 has in common with the present invention a fence-like, track-mounted gas deflector rail. However, the vehicle based components of the propulsion system are configured quite differently. The O'Connor system consists of a four stage arrangement of curved vanes with two stages operating on the reaction principle and two stages on the impulse principle. The propulsive gas stream traverses the flow deflector rail from opposing directions in succession. Other distinguishing features of the O'Connor system are the variable incidence nozzle vanes controlling the gas stream in both magnitude and direction simultaneously and which open and close to supply and shut off gas flow to the gas deflector rail. Reverse motion is achieved only to a limited extent and ineffectually, since thrust has already been generated in the first two stages by exhausting the gas forward through louvers in the front end of the duct. When the vehicle is stopped, the engine is set to idle and the blades of the power head are pivoted to the closed position to shut off gas flow across the reaction rail. While idling, the gas flow is discharged overboard through a duct controlled by a valve. The power head unit also requires its own support to ensure the necessary precise alignment of the turbine components operating on the reaction principle. The power head is therefore independently supported, preferably on an air cushion.
It will be recognized that the previously cited references disclose complex systems which would be expensive to manufacture and maintain and hence could not compete with current solutions.